Method for measuring or investigation of fiber structure (details about optical and X-ray diffraction & electron microscopy and electron diffraction method)

1. METHOD FOR MEASURING OR INVESTIGATION OF FIBER STRUCTURE
Presentation on

2. METHODS
 There are many methods for measuring of fiber structure. Such
as:
 The absorption of infrared radiation
 Raman scattering of light
 Optical and X-ray diffraction
 Optical microscopy
 Electron microscopy and electron diffraction
 Nuclear magnetic resonance
 Optical properties
 Thermal analysis
 Density
 General physical properties
 Here I only describe about optical and X-ray diffraction & electron
microscopy and electron diffraction method.

3. OPTICAL AND X-RAY DIFFRACTION
 When a beam of light is passed through a
photographic slide, the light is scattered in many
directions.
 By using a lens in the right place, we can recombine
this scattered information about the picture into an
image on a screen.
 But the information is there before it is
recombined, and diffraction is the science of
understanding and using this information in all sorts
of ways.
 Diffraction is the study of the particular patterns that
may be found when waves pass through or round
objects of particular shape.

4. OPTICAL AND X-RAY DIFFRACTION
 For example, there is a
characteristic
diffraction pattern from
a single slit. The
difference between the
image that must be
focused at a particular
place and the angular
diffraction pattern that
can be intercepted
anywhere is shown in
Fig. 1.6.

5. OPTICAL AND X-RAY DIFFRACTION
 The use of polarized light in either of the above two
techniques changes the pattern and thus, in
principle, increases the available information about
structure if it can be interpreted.
 The diffraction patterns from objects with some
regular repetitive structure are more simple and
immediately useful. Thus a diffraction grating of
regularly spaced lines, illuminated normally by
parallel light, will give a set of fringes, with the
maxima of the bright bands at angles φ defined by
the relation:
 nλ = a sinφ
 Where n is an integer, λ the wavelength of light and a the
spacing of the lines in the grating.

6. OPTICAL AND X-RAY DIFFRACTION
 X-ray diffraction is a most important tool for the study of
fiber structure,
 Firstly, because it gives information at the most important level
of fine structure; &
 Secondly, because focusing of X-rays is not possible, so that
diffraction methods have to be used.
 Three advances have made the technique more powerful
than was available to the pioneers of X-ray diffraction:
 Arrays of detectors give enhanced quantitative information on
the diffraction pattern;
 Computer software then enables the data to be analyzed and
interpreted; &
 The increased power of synchrotron radiation reduces
exposure times and allows small spot sizes to be used.

7. OPTICAL AND X-RAY DIFFRACTION
 A crystal can be regarded as
made up of layers of
atoms, themselves regular in
their two-dimensional
plan, stacked regularly on top of
one another. Although analysis
of the diffraction from such a
three-dimensional lattice is more
complicated than for a simple
grating, it does result in a very
similar equation; for it can be
shown that, if a beam of X-rays
is directed at a crystal, it is
strongly reflected whenever it
strikes layers of atoms at an
angle θ, shown in Fig. 1.8, such
that:
 nλ = 2d sinθ

8. OPTICAL AND X-RAY DIFFRACTION
 The condition that a
particular reflection
should occur is that the
layer of atoms should
make the required angle
with the X-ray beam.
This will happen for a
series of orientations of
the crystals distributed
around a cone. The X-
rays will be reflected
around a cone of twice
this angle, as shown in
Fig. 1.10.

9. OPTICAL AND X-RAY DIFFRACTION
 Layers of atoms giving rise to a
particular reflection will make a
constant angle, φ, with this crystal
axis, but, if there is no preferred
orientation perpendicular to the fiber
axis, the layers can occur at a
series of positions distributed
around the fiber axis on a cone, as
shown in Fig. 1.11. If an X-ray beam
is directed at right angles to the
fiber axis, the reflections will now
occur, not round a whole cone, but
only at those four angles at which
the cone of Fig. 1.10 (defining the
characteristic angles of reflection)
intersects with the cone of Fig. 1.11
(defining the angles at which the
particular layers of atoms occur).
This is illustrated in Fig. 1.12

10. ELECTRON MICROSCOPY AND ELECTRON DIFFRACTION
 Electrons, although usually regarded as particles, can act as if
they were waves with a wavelength of the order of 0.005 nm.
 They can be focused by bending their paths in electric and
magnetic fields in the same way that light rays are bent by lenses.
 Electron microscopes can form an image with a limit of resolution
that is far smaller than is possible with an optical microscope.
 A limitation is that the specimens must be in a vacuum.
 The early applications of electron microscopy to fibers are
discussed by Chapman, Hearle and Greer, Hearle and Simmens
and Hearle have used tomography to make a quantitative
determination of the twist angles in the helical assembly of the
intermediate filaments (micro fibrils) in the macro fibrils of the
ortho-cortex of wool.

11. ELECTRON MICROSCOPY AND ELECTRON DIFFRACTION
 Much better method for examining surface detail is scanning
electron microscopy (SEM).
 The principle of this method is that a fine spot of electrons is
traversed across the specimen and some response is used to
form an image on what is, essentially, a television screen
scanned synchronously with the spot.
 In the usual mode of operation, where the scattered electrons
picked up by a collector are used to generate the image, the
picture looks like an ordinary enlarged image of the specimen as
viewed along the column followed by the electrons forming the
spot.
 The main use of scanning electron microscopy in fiber science
has been in the range of medium to high magnification, which is
near or beyond the limit of the optical microscope.
 The scanning electron microscope has the great advantage of a
much larger depth of focus.